My all-time favorite has got to be Woody Guthrie's "TALKING HARD WORK" It's hysterical. It may be a stretch, but Ron Thomasin's intros during live performances of the Dry Branch Fire Squad are also really funny. I heard a few people complain that "ONce he gets to talkin', he forgets that he's SUPPOSED to be playin' music up there", but I think that's half of their charm. If you don't have the opportunity to see them, their "Live...At Last' CD is a must.
Rich